1. Field of the Invention
The present disclosure relates to a sheet stacking apparatus capable of stacking a large number of sheets to be discharged thereon, and to an image forming apparatus.
2. Description of the Related Art
The image formation speed of an image forming apparatus for forming an image on a sheet has recently been increased with technical advancements. Such an increase of the image formation speed has increased discharge speed of sheets to be discharged from an image forming apparatus body. Japanese Patent Application Laid-Open No. 2007-062907 discusses an image forming apparatus including a sheet stacking apparatus for aligning and stacking a large number of sheets discharged at high speed.
According to Japanese Patent Application Laid-Open No. 2007-062907, the sheet stacking apparatus has a plurality of discharge ports and independently elevatable stacking trays corresponding thereto. When sheets are stacked on the stacking tray, the stacking tray is moved down as the number of stacked sheets increases, so that the number of sheets stacked on the tray can be increased.
In such a related-art sheet stacking apparatus having the plurality stacking trays to increase the number of sheets to be stacked thereon, more sheets are arranged to be stacked on a lower stacking tray so that the stability of the sheet stacking apparatus is enhanced. Since the lower stacking tray stacks thereon more sheets than an upper stacking tray, the center of gravity of the entire sheet stacking apparatus can be positioned lower when a maximum number of sheets are stacked. Accordingly, the sheet stacking apparatus can be improved in the stability thereof.
When a large number of sheets are stacked on a lower stacking tray, however, there are cases where stackability of the stacking tray is deteriorated, therefore, a stable stack of the sheets becomes difficult.